respond_to? must take optional second argument. This was a
latent bug exposed by a recent internal change of marshal.c to
call respond_to? with a second argument; submitted by Jeremy
Kemper <jeremy at bitsweat.net> in [ruby-core:17045].
git-svn-id: http://svn.ruby-lang.org/repos/ruby/branches/ruby_1_8_7@16756 b2dd03c8-39d4-4d8f-98ff-823fe69b080e